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The V.23 standard was an early modem standard first approved by ITU-T precursor CCITT in 1964. It specifies
audio frequency-shift keying Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather ball ...
(AFSK) to encode and transfer data at a rate of 1200
bits per second In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...
, full-duplex at 1200 baud (Mode 2), (or at a "fallback rate" of 600 baud, mode 1) for the forward data-transmission channel, and an optional 75 baud backward channel. * V.23 Mode 1 AFSK uses a 1300 Hz tone (FZ) for ''mark'' (typically a binary ''1'') and 1700 Hz (FA) for ''space'' (typically a binary ''0''), and a 1500 Hz center frequency (F0). * V.23 Mode 2 AFSK uses a 1300 Hz tone (FZ) for ''mark'' (typically a binary ''1'') and 2100 Hz (FA) for ''space'' (typically a binary ''0''), and a 1700 Hz center frequency (F0). * V.23 backward channel AFSK uses a 390 Hz tone (FZ) for ''mark'' (typically a binary ''1'') and a 450 Hz (FA) for ''space'' (typically a binary ''0''). In some European countries, (and perhaps elsewhere), V.23 Mode 2 AFSK modulation, (without the backward channel) is used to transmit Caller ID information over POTS lines in the public telephone network. The 75 baud backward channel was originally envisioned for use in error correction schemes, but V.23 was also widely used in Videotex applications where the backward channel was used to send keyboard data in an asymmetrical full duplex scheme in devices such as the Minitel.


Related technology

The
BELL 202 The Bell 202 modem was an early (1976) modem standard developed by the Bell System. It specifies audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200 bits per second, half-duplex. It has separate sets of circuits fo ...
communications standard defines a similar modulation scheme.


See also

* Caller ID


References


External links


the ITU V.23 normalization
Modems Telecommunications-related introductions in 1988 V.23 {{telephony-stub